Appendix: Safe torque off (STO) 421 Activation switchIn the wiring diagram above (page 419), the activation switch has the designation (K).This represents a component such as a manually operated switch, an emergencystop push button switch, or the contacts of a safety relay or safety PLC.• If a manually operated activation switch is used, the switch must be of a type thatcan be locked out to the open position.• Inputs IN1 and IN2 must open/close within 200 ms of each other. Cable types and lengths• Double-shielded twisted-pair cable is recommended.• Maximum cable length 300 m (984 ft) between activation switch (K) and drivecontrol unit.Note: A short-circuit in the wiring between the switch and an STO terminal causes adangerous fault and therefore it is recommended to use a safety relay (includingwiring diagnostics), or a wiring method (shield grounding, channel separation) whichreduces or eliminates the risk caused by the short-circuit.Note: The voltage at the INx terminals of each drive must be at least 13 V DC to beinterpreted as “1”. Grounding of protective shields• Ground the shield in the cabling between the activation switch and the controlboard at the control board.• Ground the shield in the cabling between two control boards at one control boardonly.
